The Human Heart The human heart is a specialized, four chambered muscle that maintains blood flow in the circulatory system. The heart is located in the thorax, it lies left of the body's midline, above and in contact with the diaphragm. It is behind the breastbone, or sternum, and between the lungs, with its apex tilted to the body's cavity left side. In most people the apex can be felt during each heart contraction. When the heart is at rest, the heart pumps about 59cc (2 oz) of blood per heart beat and 5 l (5qt) per minute, compared to 120-220cc (4-7.3oz) per beat and 20-30 l (21-23 qt) per minute during exercise. The adult human heart is about the size of a f